Electric furnace and method of operating the same



G. H. sETHMAN ELECTRIC FURNACE AND METHOD 0F OPERATING THB SAME FiledJan. 30 1922 gwuenfm Patented Jan. 15, 1924.

UNITED STATES PATENT OFFICE'.

GEORGE H. SETHMAN, OF DENVER. COLORADO, ASSIGNOR, BY DIRECT AND mNE AS1-SIGNMENTS, TO THE ELECTRIC RESEARCH COHPANY, 0F DENVER, COLORADO, A

COMMON LAW TRUST.

ELECTRIC FURNACE AND METHOD 0F OPERATING THE BAIE.

Application led January 30, 1922. Serial No. 532,787.

To ai] whom t may concern:

Be it known that I, GEORGE H. SETHMAN, a citizen of the United States,residing at the city and county of Denver and State of Colorado, haveinvented certain new and useit appertains to make and use the. same,

reference being had to the accompanying drawings, and to the charactersof reference marked thereon, which form a part of this specication.

rThis invention relates to the art of smelting refractory ores, and hasspecial reference to an electrically operated furnace employing singleor polyphase current of a certain characteristic wave form.

It has long been recognized that an electric furnace for smeltingrefractory metalliferous ores would possess many advantages over thepresent extensively employed method of using'a blast furnace providedwith colte fuel. I am aware that many types ofelectrically operated,furnaces have been designed and patented and that some of them aresuccessfully employed in smelting highly conductive ores, such as ironores, but so far as I am aware, there has not been produced an electricfurnace which will successfully smelt the highly refractory auriferous,auriargentiferous, plumbiferous and other highly refractor ores whichhave little or no electrical con uctivity as compared with the highlyconductive iron ores.

Attempts to employ an electric arc furnace for smelting the above typeof ores have usually been followed by disastrous resuits, owingprimarily to the fact that the resistance of the arc path is subject tothe most violent fluctuations, varying from a very high resistance to adead short circuit.

.i In order to successfully operate an are under such variableconditions by means of the ordinary direct or alternating current, it isnecessary to equip the furnace with complicated regulating means whichwill automatically vary the voltage in an attem t to keep the currentstrength constant. uch regulating means are not reliable in operation,with the result that troublesome surges, kick-backs, and intermittentdisturbances take place, which damage the generators and transformersand make it a practical` mpossiblity to carry out the smeltingsucces'sfully.

I have found-that if I employ,as the source of electric current supply,a generatorwhich generates a flat top expanding wave,

due to the fact that at no time after the first part of the voltage andcurrent waves are producedis there any dynamic action between the fieldsand the armature, that in a circuit supplied with current by such agenerator, extreme variations in the arc resistance and. even shortcircuits can take place without injuring the generator, blowing fuses,opening circuit breakers, throwing off the belts on belted units, ordistress- -ing the engine or generator, in the case of units of thedirect connected type. It is the employment of the above type of currentgenerator that has enabled me to ,successfully smelt highly refractoryores without employing any regulating devices whatever for thepurpose ofcompensating for the vanations in the arc resistance, and wi-thout asource of current supply having the above characteristics, an' electricarc furnace for smelting this class of ores is not regarded ascommercially practicable.

In order to describe myinvention with the greatest degree of clearness,I shall have reference to the accompanying drawing, in which- Y Fig. lis a da ram showing the characteristic voltage an current wave producedby the generator which I employ in this smelting process;

Fig. 2 is a diagram showinghow a three- `phase Y connected source ofcurrent supply is connected to the smelter electrodes;

Fig. 3 is a vertical longitudinal section of one form of smelteremployed by me;

lll

onsidering (D as the point of origin, curve E extends upwardly in adirection which corresponds somewhat to that which would be followed byan ordinary sine curve until the point D is reached when it becomesparallel to the longitudinal anis @-1- K for a short time until thepoint lds 1s reached. it this point all dynamic action between thearmature and the fields of the generator ceases and the voltage curveextends downwardly to the axis on a line that corresponds to alogarithmic curve. Fllhe current curve C follows the general shape ofthe voltage curve E and attains itspzero value at the same instance asthe voltage curve. ln case of a low arc resistance or dead shortcircuit, no serious damage can result when a generator producing apotential curve of the above described type is employed, for the reasonthat during the part of the curve from O to D the value of the currentis limited by the counter electromotive force of self induction, whileafter the point l? is passed, the electromotive force is merely thatwhich is due to the inductive kick or stored energy of the windin s,

glu `Fig. 2 l have shown a source of threephase supply G in which thephases a, h and c are connected Y fashion. The neutral point of thegenerator is connected by means of a conductor 2 with a plate electrode3 which is located in the bottom of the furnace. lhe free ends of therespective phases a, b and c are connected respectively with electrodesll, 5 and 6 by means of conductors 7, 8 and 9. l have shown athree-phase supply because this is the simplest and serves to illustratethe arrangement as well as any other number of phases, but l desire topoint out that it is my intention to employ any number of phasesdesired` as for example,

- two, three, sin, nine and twelve, the exact number being dependenton-thc size of the lili Bil

smelter and other elements which will determine the design of thelayout.

lin Fig. 3 l have shown one form of furnace which l consider welladapted for use in carrying out my method. The furnace l0 is built oflire brick or anysuitable refractory substance, and has its base portionll enlarged to some extent; the upper part of the furnace has acylindrical opening l2 therein which terminates at the bottom in anenlarged furnace space l, in the bottom of which is formed a pocket ordepression 1li within which is placed a copper plate 3 whose uppersurface is provided with a number of copper points l5. The pocket 1t isiilled with graphite so as to form a conductive protective cover for thecopper electrode 3. Projecting through the inclined walls 17 of thefurnace l0 are a plurality of electrodes, the exact number of whichdepends on the number of phases employed; these agencer electrodes areequally spaced and when three arc employed, as in the exampleillustrated, they are spaced 120 degrees apart. "Where the electrodesenter the furnace, they pass through stuffing boxes V18 which arepreferably hollow and adapted to he cooled by the circulation of waterthrough thc hollow interior thereof. The electrodes are slidable in theboxes 18 so as to permit of adjustment being made.

The chamber 18 is provided near the bottom thereof with two spouts 19and 20, the former of which is located near the bottom of the chamberand serves for removingthe matte. while the spout 2O is located somewhathigher and serves for removing the slag, the separation of the slag andina-tte being effected by the action of gravity which causes the matte,which is heavier, to sink to the bottom of the liquid mass. Near the topof the furnace l provide a hollow conduit 21 which extends to and isconnected with a condenser (not shown). The top of the furnace iscovered by a plate 22, whichl is provided centrally thereof with acylindrical member 23 of considerable length, the lower end of whichprojects into the furnace and is provided with a closing cone 2li, whichis pivotally connected to one end of pivotally mounted lever 25, on theouter end of which is a weight 26. rlhe ore is fed to the fur-- nacethrough the tube 23 in the well known manner. @n the sides of thefurnace l have provided several hoppers 27 which can be employed foradding material to the furnace. lf it should he found desirable, fuelmay be added to the ore through hoppers 27 and used to increase thepreheating effect. Line V28 vindicates the proper level of ore in thefurnace.

ln Fig. d l have shown a slightly modified form of furnace, whichdiffers from the one described above. mainly, in this, that aconsiderable space is provided between the lower edge of the opening ofthe matte spout and the top of the graphite packing 16, which space isdesigned to con-tain the molten lead. which :may be removed from time totime through opening 29, or which may automatically overiiow over edges30 whenever it env ceeds the level of this edge.

Although l have shown and described in detail a furnace structure, it isevidentthat `furnaces of different forms may be einployed with myparticular current supply. rllhe furnace described above is, however, asatisfactory and practical device, and l reserve the right to protectthe same in this or in a divisional application.

The operation of my furnace is as follows: The electrical connectionsare formed 'as indicated on the drawing and explained above. Anelectrically conducting ore or other electrically conducting material isthen placed inv the furnace and about and between electrodes 4, 5, 6.and 1G, so that when the electromotive force is applied, current willbegin to flow between the electrodes. Ore and fluxes are then introducedinto the furnace in the proper proportions and in such amounts asdesired. not extending above line 28. The current is then applied andows through the conducting material from the several electrodes to plate3. The current flowing through -the conductive material causes thelatter to become intensely heated and very soon melts the same, afterwhich the arc having become established continues to burn and heat therefractory ores that feed down from above. down carries a small portionof the current, as it is not an absolute non-conductor, and heat istherefore generated by the current iiowing through the mate-rial as wellas by the arc. Both forms of heat are therefore generated and utilizedin the reduction. lVhen the condenser is attached' and operated,-astrong fan (not shown) will be in operation and arranged to suck thegases from the furnace through pipe 21, and the hot gases from aroundthe arc will'pass upwardly, roasting and preheating the ,ore so that bythe time it reaches the arc chamber' 13 it will be heated to very nearthe melting point. lBy having the chamber 12 of Sullicient length, thegases may be cooled to a comparativelylow degree before they leave thefurnace-,thus assuring a very thorough vutilization of all the heatgenera-ted. The

spouts 19 and 20 may be leftopen so that 'the slag and matte may'flowfrom the furnace as fast as they are formed, thus providing forcontinuous operation.

My smelting furnace can be made of any desired size and capacity,'andsmall units can be cheaply and easily constructed. It therefore 4becomespossible for mines that are 'located far from a railroad or a fuelsupply to be equippedwith electric smelters, the current for theoperation of which can be supplied by an internal combustion enginedriving one of my specially designed gen-k erators referred to above. Asfuel for the operation of the engine can be readily transported, it isapparent that mines that heref tofore have been idle owing to theexcessive cost of transporting the ore to a smelter, can be operated,and the ore smelted electrically. The matte can then be sent to arefinery where it canbe separated into the` several metals of which itis composed. Large custom smelters can also be operated as de-` scribedabove, and at a cost per ton of o're greatly less than what it is withthe present coke blast furnace. v Y

'As pointed out above, I do not claim to be the first one to haveemployed electricity for smelting ores, but I do claim that I havediscovered the proper form, of potential and current wave to be employedin the suc- The ore as it comes" land. as this 1s a common specific formof current wave and an electric arc furnace, as the two cooperate toproduce a result long desired and often sought but never beforeattained.

The voltage will be anything that may be found necessary to Iproduce thearc between the electrodes and the bottom plate 3, and ordinarily itisabout 145 volts, while the amperage will run from 250 in small furnacesto several thousand amperes in the larger furnaces. The frequency isalso more or less optional, but cycles is satisfactory,

' frequency, it is employed in this combination by me.

Having now described my invention, what I claim as new is 1. In anelectric furnace for the'smelting 2. The method of smeltin highlyrefractory metalliferous ores, w ich comprises subjecting the same tothe heating effect of an arc between a plurality of electrodes,supplying a multiphase electric current to said electrodes, said currenthaving a potential whose wave form is such that its front face iscomparatively steep, its top is substantially flat, and whose rear'isupwardly concave.

3. The method of smelting ores in an electric arc furnace having aplurality of electrodes adapted to be connected to and operated by a Yconnected source of polyphase current, which consists in supplying saidelectrodes with a current whose potential wave form is such that its topis comparatively flat and whose rear is upwardly concave.

4. The method ofv smelting ores in an electric arc furnace, having aplurality of electrodes adapted to be connected to and operated by aYeconnected source of polyphase current, which consists in supplyingsaid electrodes with a current whose potential wave form is such thatits front face is substantially sinusoidal, whose top is flat,

and whose rear face is substantially a loga l UU the neutral point ofsaid phases, and a polyphase generator in which the interaction betweenthe armature windings and the eld is such that duringr the first partot" each alternative, the voltage produced follows rent, one electrodeadapted to be connected to the neutral point or said phases, and apolyphase generator in `which the interaction between the arma-turewindings and the field is such that the power 'factor is Substantiallyone.

7. The method of smelting ores in an electric arc furnace having aelectrodes, which consists in supplying said electrodes with a currentWhose potential Wave form is such that its front face is substantiallysinusoidal, Whose top is Hat, and Whose rear tace is substantially alogarithinetic curve.

ln testimony 'whereof l affix my si nature.

GEORGE H. SETH fl'AN.

plurality ot"

